Switching data signals of at least two types for transmission over a transport network providing both backhaul and fronthaul (Xhaul)connectivity

ABSTRACT

A method for switching data signals transmitted over a transport network is disclosed. The method comprises receiving a plurality of input data signals of a first signal type wherein the plurality of data signals of the first signal type comprises data signals exchanged between a Radio Equipment and a Radio Equipment Controller and aggregating the plurality of input data signals into an aggregated first data signal. The method also comprises receiving a second data signal of a second signal type different to the first signal type, and multiplexing the first data signal with the second data signal to form a combined data signal. The method further comprises forwarding the combined data signal to the transport network. Multiplexing the first data signal with the second data signal comprises, for a frame of the combined data signal, allocating the first data signal to a portion of the frame reserved for the first data signal, and allocating the second data signal to a remaining portion of the frame.

TECHNICAL FIELD

The present disclosure relates to a method for switching data signalsfor transmission over a transport network. The present disclosure alsorelates to an apparatus for switching data signals for transmission overa transport network, and to a system for exchanging data signals.

BACKGROUND

In cellular communication networks, radio base stations (RBS) provideradio network coverage over a coverage area or cell. Communication linksbetween the RBSs of a network and the communication network core segmentare referred to as the Mobile Backhaul (MBH) or backhaul. In traditionalarchitectures, both radio and baseband processing are performed in theRBS, which outputs an Ethernet signal which is then transported over theMBH using microwave and/or optical fibre. In some implementations, RBSsmay be separated into one or more radio units and one or more basebandprocessing units, enabling, among other advantages, the optimising ofradio unit placement. The radio units may be referred to as Remote RadioUnits (RRUs) or as Radio Equipments (REs). The baseband processing unitsmay be referred to as Digital Units (DUs) or as Radio EquipmentControllers (RECs). The communication links between REs and RECs in suchdeployments are collectively referred to as the Mobile Fronthaul (MFH)or fronthaul, and the interface between REs and RECs is referred to inthe following specification as the Fronthaul Interface (FHI). The CommonPublic Radio Interface (CPRI) specifies an interface protocol for theFHI, managing RBS communication between REs and RECs.

The Xhaul paradigm proposes the combination of MFH and MBH in a commonconnectivity segment, with the aim of implementing the technologicalshift that will be required of 5G communication networks. Xhaul proposesthe concurrent transport of CPRI traffic from REs towards a centralisedREC pool and Ethernet traffic from conventional RBSs towards furtheraggregations stages.

5G networks will be required to accommodate exponential increases inbandwidth usage compared to current levels. Owing to the bandwidthintensive nature of CPRI, this increase in bandwidth is likely to renderthe use of CPRI impractical for fronthaul communications: CPRI bandwidthcan be up to 30 times higher than equivalent radio signal bandwidth,meaning for a 10 Gbps radio signal, CPRI could attain 300 Gbps, whichcannot be managed.

SUMMARY

According to a first aspect of the present disclosure, there is provideda method for switching data signals transmitted over a transportnetwork; the method comprising receiving a plurality of input datasignals of a first signal type wherein the plurality of data signals ofthe first signal type comprises data signals exchanged between a RadioEquipment (RE) and a Radio Equipment Controller (REC). The methodfurther comprises aggregating the plurality of input data signals intoan aggregated first data signal, receiving a second data signal of asecond signal type different to the first signal type and multiplexingthe first data signal with the second data signal to form a combineddata signal. The method further comprises forwarding the combined datasignal to the transport network. Multiplexing the first data signal withthe second data signal comprises, for a frame of the combined datasignal, allocating the first data signal to a portion of the framereserved for the first data signal, and allocating the second datasignal to a remaining portion of the frame.

Thus, different signal types including data signals between a RE andREC, are efficiently transported.

According to examples of the disclosure, the aggregated first datasignal and the combined data signal may be synchronised with a referencetiming signal, and/or multiplexing the aggregated first data signal withthe second data signal to form a combined data signal may compriseperforming time division multiplexing of the aggregated first datasignal with the second data signal.

According to examples of the disclosure, the second input data signalmay comprise a data signal exchanged between a Radio Base Station (RBS)and a core network.

According to another aspect of the present disclosure, there is providedapparatus for switching data signals transmitted over a transportnetwork; the apparatus comprising a plurality of ports configured toreceive a plurality of input data signals of a first signal type whichare exchanged between a RE and an REC, and a first switch configured toaggregate the plurality of input data signals into an aggregated firstdata signal. The apparatus further comprises a port configured toreceive a second data signal of a second signal type different to thefirst signal type, a multiplexing switch configured to multiplex thefirst data signal with the second data signal to form a combined datasignal, and an interface configured to forward the formatted combineddata signal to the transport network. The multiplexing switch comprisesa framer configured, for a frame of the combined data signal, tomultiplex the first and second data signals by allocating the first datasignal to a portion of the frame reserved for the first data signal, andallocating the second data signal to a remaining portion of the frame.

According to another aspect of the present disclosure, there is providedapparatus for switching data signals transmitted over a transportnetwork; the apparatus comprising a processor and a memory, the memorycontaining instructions executable by the processor whereby theapparatus is operative to receive a plurality of input data signals of afirst signal type wherein the plurality of data signals of the firstsignal type comprises data signals exchanged between a Radio Equipment(RE) and a Radio Equipment Controller (REC) and aggregate the pluralityof input data signals into an aggregated first data signal. Theapparatus is further operable to receive a second data signal of asecond signal type different to the first signal type, multiplex thefirst data signal with the second data signal to form a combined datasignal, and forward the combined data signal to the transport network.Multiplexing the first data signal with the second data signalcomprises, for a frame of the combined data signal, allocating the firstdata signal to a portion of the frame reserved for the first datasignal, and allocating the second data signal to a remaining portion ofthe frame.

According to another aspect of the present disclosure, there is provideda system for exchanging data signals, the system comprising a firstapparatus according to the second or third aspects of the presentdisclosure, the first apparatus configured as a hub node and operable toreceive input data signals from an REC and a router, a second apparatusaccording to the second or third aspects of the present disclosure, thesecond apparatus configured as a remote node and operable to receiveinput data signals from an RE and an RBS, and a transport networkcoupled between the first apparatus and the second apparatus. The firstapparatus is configured to transmit data signals of the first and secondtype over the transport network to the second apparatus, and the secondapparatus is configured to transmit data signals of the first and secondtype over the transport network to the first apparatus.

According to another aspect of the present disclosure, there is provideda computer program comprising instructions which, when executed on atleast one processor, cause the at least one processor to carry out amethod according to the first aspect of the present disclosure.

According to another aspect of the present disclosure, there is provideda carrier containing a computer program according to a preceding aspectof the present disclosure, the carrier comprising an electronic signal,an optical signal, a radio signal or a computer readable storage medium.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present disclosure, and to show moreclearly how it may be carried into effect, reference will now be made,by way of example, to the following drawings in which:

FIG. 1 is a block diagram illustrating elements in a system forexchanging data signals;

FIG. 2 is a flow chart illustrating process steps in a method forswitching data signals transmitted over a transport network;

FIG. 3 is a block diagram illustrating functional units in a switchingapparatus;

FIG. 4 is a block diagram illustrating a hub node;

FIG. 5 is a block diagram illustrating a remote node;

FIGS. 6a and 6b illustrate operation of a multiplexing switch in the hubnode of FIG. 4 or remote node of FIG. 5; and

FIG. 7 is a block diagram illustrating functional units in anotherexample of switching apparatus.

DETAILED DESCRIPTION

In order to address the conflict between the bandwidth intensive natureof CPRI and the bandwidth requirements for 5G, a new division of radioprotocols may be used for REs and RECs, moving physical layer (L1)processing “back” to the RE. An RE operable to perform L1 processing isreferred to the rest of the present disclosure as a modified RE, orRadio Baseband Unit (RBU), and an REC cooperating with such a modifiedRE is referred to as a modified REC or Baseband Unit (BBU). Theinterface between a modified RE and modified REC is referred to in thepresent disclosure as the Modified Fronthaul Interface (MFI). The MFIbetween RBU (i.e. RRU) and BBU is a packet interface. The packet basedMFI protocol is for fronthaul, e.g. configured to carry radio datacorresponding to radio frequency data for transmission. The MFI packetscarry radio data allowing generation of the radio frequency signal fortransmission at the RBU (i.e. RRU), and received radio data requiringbaseband processing in a BBU. The MFI packets are not encapsulated to bein the form of packets; MFI is a packet interface. Switching solutionsfor an Xhaul connectivity segment may therefore be required to deal bothwith legacy CPRI signal flows (not packet based) and with packet basedprotocols from e.g. backhaul (e.g. Ethernet) and the new packet basedfronthaul interface (e.g. the protocol referred to as MFI).

Packet switches offer the advantage of managing both Ethernet and thenew packet based Fronthaul protocols in the same switching engine.However, Packet Delay Variation (PDV) and delay control are difficult tomanage when both these signals are processed by the same switch. TheIEEE 802.1 Time-Sensitive Networking Task Group (TSN TG) is studyingthis problem, but there are issues with latency (in the case of multipleswitching hops), with deterministic delay to be ensured downstream andupstream, with PDV, and with synchronization distribution.

Circuit switches deal with jitter and delay control better than packetswitches, but cannot offer statistical multiplexing gain, which isuseful to handle traffic loads of the orders expected in 5G. 5G trafficis expected to be characterized by a highly bursty distribution, withpeaks as high as 10 Gbps per sector and average traffic as low as 200kbps. Without statistical multiplexing, a network serving 100 sectorsmight require 1 Tbps. Introducing statistical multiplexing allowsdimensioning of the network to accommodate one peak, i.e. 10 Gbps, and100 times the average traffic, i.e. 20 Mbps.

Aspects of the present disclosure provide a layered switchingarchitecture and method according to which input data signals ofdifferent signal types may be forwarded for transport over a transportnetwork. Examples of the layered switching architecture and method mayenable exploitation of statistical multiplexing gain while also ensuringdeterministic delay and low PDV in the implementation of combinedFronthaul and Backhaul communications. The architecture and method mayinvolve packet, Time Division Multiplexing and transport networkelements. An implementation of the architecture may involve a firstswitching apparatus, acting as a hub node, and a second switchingapparatus, acting as a remote node. Each of the hub and remote nodes maycomprise first, second and third stages as discussed below.

Considering a hub node, the node may comprise a first stage includingone or more independent switches, each switch handling one homogenoustype of signal. For example, a first independent switch may handle MFIsignals, a second independent switch may handle legacy radio signalssuch as CPRI signals and a third independent switch may handle Ethernetsignals. Different MFI or CPRI implementations, for example as may beprovided by different vendors, may be managed by dedicated switches. Theoutput of each switch may be made time synchronous by providing anexternal timing reference. In some examples, the circuit switchedfronthaul data signal is converted to a packet switched format. In someexamples, the CPRI switch may include an InterWorking Function (IWF) sothat the output frame has an Ethernet format.

A second stage of the hub node may comprise a Time Division Multiplexing(TDM) switch, which receives as input the output of the switches of thefirst stage and assigns these first stage outputs time slots in a frame.The second stage TDM switch may receive the same or common externaltiming reference as the first stage switches, enabling synchronousoperation.

A third stage of the hub node may comprise an interface for formattingthe output of the TDM switch for transport over the relevant transportnetwork. In the case of an optical transport network, this formattingmay include assigning reconfigurable wavelengths to the TDM framesoutput by the TDM switch. Other formatting examples may be envisaged fordifferent transport network types.

A switching apparatus acting as a remote node may include complementaryfirst, second and/or third stages to those described above in thecontext of a hub node. The hub node and remote node may thus act torender packet traffic synchronous with the use of an external timingreference, so enabling the control of delay and the minimization of PDV.The hub node communicates with one or more remote nodes over a transportnetwork, e.g. an optical network. The transport network is a fronthaulnetwork between one or more RE and one or more REC, and also providesfor communication (i.e. backhaul) between a RBS having integratedbaseband processing and a core network. Packet traffic may beencapsulated in standard Ethernet and standard transport networkformatting to ensure full interworking with current networks.

FIG. 1 illustrates an example system comprising a hub node 40 and aplurality of remote nodes 60 as described above. The connectivity of oneof the remote nodes 60 is shown in greater detail for the purposes ofillustration. In the example system of FIG. 1, the transport network 50via which the hub and remote nodes 40, 60 communicate implements Xhaulconnectivity between, on one side, one or more baseband processing unit(e.g. BBUs processing packet MFI signals, one or more DUs processingnon-packet radio signals such as CPRI), and a packet switch/router 10for backhaul traffic, and on another side, a plurality of RBUs, RRUsand/or RBSs (i.e. REs and/or RBSs).

The hub node 40 and remote nodes 60 are coupled by a transport network50 providing both backhaul and fronthaul (i.e. Xhaul) connectivity. Insome examples, the transport network 50 is an optical network. Forexample, the optical network between the REs and RECs comprises opticallinks, e.g. optical fibers, and the signals are carried in an opticalformat. Some examples employ OTN technology or may employ othertechnology such as Synchronous Digital Hierarchy (SDH), WavelengthDivision Multiplexing (WDM), TDM, Ethernet etc.

The hub node 40 is connected to one or more baseband processing units,e.g. BBUs, which may be comprised within a BBU pool 20, from which itreceives a plurality of first data signals in the form of MFI datasignals. The hub 40 is optionally also connected to one or more furtherbaseband processing units, e.g. DUs, which may be comprised within a DUpool 30, from which it receives a plurality of third data signals in theform of digitized radio signals, for example CPRI signals. The hub 40 isalso connected to a packet router 10, from which it receives a seconddata signal in the form of backhaul packet signal, which may for examplecomprise Ethernet traffic.

The hub 40 comprises a timing controller which exchanges referencetiming information with timing controllers in each remote node 60, forexample, generated or received using Synchronous Ethernet or IEEE 1588protocols.

Each remote node 60 is connected to one or more RBUs 70, from which theremote node 60 communicates MFI signals. The remote nodes 60 are alsoconnected to one or more RRUs 80, from which the remote nodes 60 receivea plurality of non-packet radio signals, for example CPRI signals. Theremote nodes 60 may further be connected to one or more RBSs 90, fromwhich the remote nodes receive backhaul traffic, which may for examplebe Ethernet traffic. In some examples, the system may handle anycombination of one or more of the first, second and/or third datasignals.

FIG. 2 illustrates an example method 100 for switching data signalstransmitted over a transport network. The steps of method 100 may beconducted in a switching apparatus, which may be acting as a hub node 40or as a remote node 60, as illustrated in the example system of FIG. 1and as explained in further detail below with reference to FIGS. 3 to 7.

Referring to FIG. 2, in a first step 110, the method comprises receivinga plurality of input data signals of a first signal type. The pluralityof data signals of the first signal type comprise data signals exchangedbetween a Radio Equipment (RE) and a Radio Equipment Controller (REC),and each data signal may be exchanged between a dedicated RE and REC,which REC may be comprised within an REC pool comprising a plurality ofRECs. In some examples, the data signals may comprise packet datasignals. Layer 1 processing of the packet data signals may be performedat the RE. The RE and REC may thus be a modified RE or RBU and modifiedREC or BBU, with both radio and L1 processing being performed at the RE.The first data signals may be referred to as MFI signals. The firstsignal type (e.g. MFI) may be radio data, providing signals fortransmission or receiving at radio frequencies by an antenna. Forexample, the radio data may be I/Q data. The radio data may be digitizedor analog. The first signal type may comprise data carried in packetsbetween the modified RE and modified REC (also termed RBU and BBU). Theradio data is processed by the REC to convert to/from a baseband signal.The packet fronthaul data protocol referred to as MFI may be generatedand/or received at the RE and/or REC in a packet format. The MFI formatof radio data may provide a same or similar function to CPRI, exceptbeing a packet format.

The plurality of input data signals of the first signal type may besubject to a delay specification as illustrated in step 110 a, which maycomprise one or more delay or latency requirements, each delay orlatency requirement applying to a specific one of the plurality of inputdata signals. In the case of MFI signals between a modified RE and REC,the signals may be subject to stringent latency requirements to ensureadequate service performance. In some examples, the method may furthercomprise receiving the delay specification from the REC or from the poolof RECs.

Following receipt of the first plurality of data signals, the method 100then comprises, at step 120, aggregating the plurality of input datasignals into an aggregated first data signal. This aggregation step maybe performed in one or more dedicated switches and constitutes a part ofthe first stage described above. In this first stage, signals ofdifferent types are independently handled by different switches. Forexample, a first stage switch handles aggregation/switching of MFIsignals, and a separate first stage switch handles aggregation/switchingof non-packet fronthaul signals (e.g. CPRI) and/or a separate thirdstage switch handles aggregation/switching of packets backhaul signals.

In some examples, the first stage aggregation may combine data fromdifferent ones of the plurality of input data signals of the same type.The aggregated signals may be aggregated into the same frame of theaggregated first data signal, or the aggregation may be spread over aplurality of different frames of the aggregated first data signal. Thismay be the case for each type of data signals.

The aggregated first data signal may in some examples be synchronisedwith a reference timing signal, which may be generated or received aspart of the method 100, for example the method 100 may further comprisereceiving or generating the reference timing signal via a SyncE or usingIEEE 1588 protocol or in some other appropriate manner.

Step 120 may be performed in a dedicated packet switch, and may involvethe step 120 a of performing statistical multiplexing of the pluralityof input data signals. Statistical multiplexing may comprise determininga total bandwidth of the input data signals which may be shared betweenthe plurality of input data signals according to the demand of each datasignal. Thus, each data signal is not allocated a static bandwidthallocation, but shares a common allocation. The total bandwidth may bebased on the predicted instantaneous traffic demands of the plurality ofinput data signals. Based on the assumption that not all of the inputdata signals is using maximum traffic, the allocated total bandwidth maybe lower than that indicated by summing individual data signalrequirements. In some examples, statistical multiplexing may beconsidered as dividing the aggregated first data signal into anarbitrary number of variable bit-rate digital channels or data streamscorresponding to the plurality of input data signals, and adaptingallocation of bit-rate to the different channels according to theinstantaneous traffic demands of the plurality of input data signals.

The statistical multiplexing may be performed within a limit ofcompliance with the delay specification to which the plurality of inputdata signals is subject, as shown in step 120 b. For example, thestatistical multiplexing is carried out according to the delay and/orlatency requirements.

In step 130, the method 100 comprises receiving a second data signal ofa second signal type different to the first signal type and which is notsubject to the delay specification which may apply to the plurality ofinput signals of the first signal type. In some examples, the secondinput data signal may comprise a packet (e.g. Ethernet) data signalexchanged between a Radio Base Station (RBS) and a core network, asshown in step 130 a. In some examples, a plurality of sub-signals of thesecond data signal may be received in step 132, for example frommultiple RBSs, and the method 100 may further comprise assembling thesub-signals to form the second input data signal in step 134. Aspreviously, the sub-signals may be assembled by combining differentsub-signals in a single frame of the second input data signal or byspreading different sub-signals over different frames of the secondinput data signal. Each sub-signal may be exchanged between a differentRBS and the core network. The step of assembling the sub-signals to formthe second input data signal may be performed in one or more dedicatedswitches and also constitutes a part of the first stage described above,in which signals of different types are independently handled. Thesecond signal type is carrying backhaul for communication with the corenetwork. Thus, the second signal type is not subject to the samedelay/latency requirements of the first signal type, which is carryingpacket radio data for fronthaul.

In some examples, the method 100 may further comprise the step 136 ofreceiving a plurality of input data signals of a third signal type,different to the first and second signal types and which may also besubject to a delay specification. As shown in step 136 a, the pluralityof input data signals of the third signal type may for example be radiosignals such as CPRI signals exchanged between an RE and an REC, whichmay be comprised within an REC pool comprising a plurality of RECs. Themethod 100 may further comprise the step 138 of multiplexing theplurality of input data signals of the third signal type into a thirddata signal which is synchronised with the reference timing signal. Insome examples the multiplexing may combine data from different ones ofthe plurality of input data signals of the third signal type into thesame frame of the third data signal, or the multiplexing may be spreadover several different frames of the third data signal.

Step 138 may also comprise converting the third data signal to a packetformat such as an Ethernet format, for example through the applicationof an IWF. The step of multiplexing the plurality of input data signalsof the third signal type into a third data signal may be performed inone or more dedicated switches and also constitutes a part of the firststage described above, in which signals of different types areindependently handled.

In step 140, the method 100 comprises multiplexing the first data signalwith the second data signal, and the third data signal if received, toform a combined data signal. In some examples, the multiplexing issynchronised with the reference timing signal. The multiplexing step 140may be performed in a further multiplexing switch, and constitutes thesecond stage described above, in which a multiplexing switch receives asinput the output of the switches of the first stage and assigns thesefirst stage outputs to portions of a frame. The multiplexing step 140comprises, in step 142, allocating a portion, for example a packet, fromthe first data signal to a portion of a frame of the combined datasignal reserved for the first data signal. The portion or packet of thefirst data signal selected for allocation may be selected to ensurecompliance with the delay specification to which the first plurality ofinput data signals may be subject, as shown in step 142 a.

The multiplexing step 140 may then comprise, if the third data signalhas been received, allocating a portion such as a packet from the thirddata signal to a portion of the frame reserved for the third data signalin step 144. Again, a portion or packet may be selected to ensurecompliance with the delay specification to which the third data signalis subject. The multiplexing step 140 then comprises allocating aportion such as one or more packets from the second data signal to aremaining portion of the frame in step 146. As noted above, the seconddata signal may not be subject to the same stringent delay requirementsas the first and third data signal types, and thus may be used to fillany remaining resource available in the frame once the first (andoptionally third) data signals have been allocated.

In some examples of the invention, the multiplexing step 140 may beperformed as a time division multiplexing in a TDM switch. The reservedand remaining portions of the combined data signal frame may be timeslots. Thus, the first, second and/or third data signals may be arrangedin a transport frame according to time slots, i.e. may be time divisionmultiplexed. The TDM switch may provide for transport over a circuitswitched channel (e.g. an optical channel). The radio data carried bythe first (and optionally third) data signals have reserved timeallocations within the frame. Thus, the packets of different types ofdata (e.g. radio data, backhaul data) of the first and third datasignals are carried as time multiplexed signals within the same frame.In some examples, the time slots may be allocated at multiples of thereference timing signal used in earlier aggregating steps, as describedin further detail below with reference to FIGS. 6a and 6b . Themultiplexing 140 generates a frame which comprises signals of more thanone type, e.g. one or more of the first, second and/or third type. Thesignals of the first, second and/or third type have themselves beenseparately aggregated in a first stage from a plurality of sources of aparticular type, e.g. a plurality of first type signals (e.g. MFI).

Once the combined data signal has been formed, the method 100 maycomprise, in step 150, formatting the combined data signal fortransmission over the transport network, and, in step 160, forwardingthe formatted combined data signal to the transport network. In someexamples, the transport network may be an optical network, e.g. usingOTN for transport. The formatting step 150 may comprise assigningreconfigurable wavelengths to frames of the combined data signal in step150 a. In other examples, alternative transport network technologies maybe envisaged, including Synchronous Digital Hierarchy (SDH), TDM,Ethernet etc. In some examples, the transport network may use anysynchronous transport protocol, including OTN or Synchronous Ethernet(SyncE) as described above. In such cases appropriate formatting stepsmay be performed at step 150 to enable transport of the combined datasignal over the transport network. The formatting step 150 constitutesthe third stage described above, in which a combined data signal isformatted for transport over the relevant transport network. The stepsof the first, second and third stages described above thus allow acorresponding switch to receive and distribute the data to its intendeddestination.

It will be appreciated that the above described method steps illustratea switching method in which multiple different signal types are combinedfor transporting over a transport network. The method 100 may furthercomprise steps facilitating receipt of a combined data signal,extraction of the component data signals and switching of the componentdata signals to their intended recipients. For example, the method 100may further comprise receiving a combined data signal from the transportnetwork, formatting the received signal for processing anddemultiplexing in a second stage the formatted received signal into afirst data signal and a second data signal, and in some examples a thirddata signal. The demultiplexed signals are transmitted to differentswitches according to their type, i.e. first signal type packets areswitched to a dedicated first signal type switch, second signal typepackets to the packet switch/router 10, and third signal type data tothe third signal type switch.

The method may also comprise disaggregating in a first stage the firstdata signal into a plurality of first data signals, demultiplexing thethird data signal into a plurality of third data signals, and outputtingthe plurality of first data signals, the plurality of third datasignals, and the second data signal. This disaggregating ordemultiplexing occurs in separate switches according to the differentprotocols carried in the same frame. The process of demultiplexing theformatted received signal may comprise, for a frame of the formattedreceived signal, extracting a packet to the first data signal from aportion of the frame reserved for the first data signal, extracting apacket to the third data signal from a portion of the frame reserved forthe third data signal, and extracting packets to the second data signalfrom a remaining portion of the frame. From the extracted data signalsof a particular type, e.g. first data signal, the first stage splits thesignal into the separate destinations for each of the component firstdata signals. Thus, a plurality of nodes (e.g. RBU, BBU) may communicateat the same time using the described system, with the plurality of flowsof the same type separated/combined in a dedicated switch as a separatestep to separating/combining with a different data type.

FIG. 3 illustrates a switching apparatus 200, which may conduct thesteps of the method 100, for example on receipt of suitable instructionsfrom a computer program. It will be appreciated that the unitsillustrated in FIG. 3 may be realised in any appropriate combination ofhardware, firmware and/or software. For example, the units may compriseone or more processors and one or more memories containing instructionsexecutable by the one or more processors. The units may be integrated toany degree. The switching apparatus 200 corresponds to either of the hubnode 40 or the remote node 60 discussed above with reference to FIG. 1.The description below provides examples of transmission by a switchingapparatus 200 as the hub node; transmission as the remote node andreceiving as the hub node or remote node are also briefly describedbelow and may be understood to function in a corresponding manner.

Referring to FIG. 3, the switching apparatus 200 comprises a pluralityof ports 210 configured to receive (or output, in the case of receptionoperation) a plurality of input data signals of a first signal type ofradio data. The plurality of input signals of the first signal type maybe subject to a delay specification. The plurality of ports may beconfigured to receive a plurality of input data signals each exchangedbetween an RE and an REC. As discussed above, the first input datasignals may be packet data signals of MFI traffic exchanged between aradio unit (RE, RRU or RBU) and a baseband processing unit (e.g. REC, DUor BBU) over the transport network.

The switching apparatus 200 may also comprise a timing function, in theform of a timing controller 270 which may be configured to provide atiming reference signal. The timing controller may generate or receivethe timing reference signal, for example via a SyncE or IEEE 1588protocol or in some other appropriate manner. The timing controller 270may be further configured to receive the delay specification for theplurality of data signals of the first signal type, for example from aREC or pool of RECs, alternatively, the delay specification for theplurality of data signals of the first signal type may be received by amultiplexing switch 240, as described below.

The switching apparatus 200 comprises a first switch 220, which may be apacket switch, and is configured to aggregate the plurality of inputdata signals into an aggregated first data signal. The aggregated firstdata signal may in some examples be synchronised with the referencetiming signal. The ports 210 are connected to the first switch 220 todeliver the plurality of first data signals to the first switch 220. Thefirst switch 220 may be configured to perform statistical multiplexingof the plurality of input data signals, and in some examples may performstatistical multiplexing within a limit of compliance with the delayspecification to which the plurality of input data signals is subject,and as determined for example using the timing controller 270.

The first switch 220 is thus configured to aggregate a plurality offirst data signals (e.g. fronthaul packet radio signals) received on theports 210, each signal corresponding to a particular RE or a particularREC. Correspondingly, when receiving data traffic over a transportnetwork, the first switch 220 is configured to separate component datasignals of the combined data signal of the first signal type, and toswitch each component data signal to the appropriate port for basebandprocessing (or radio transmission).

The switching apparatus 200 also comprises a port 230 configured toreceive or output a second data signal of a second signal type differentto the first signal type and which is not subject to the delayspecification. The second data signal may be a packet (e.g. Ethernet)data signal exchanged between an RBS and a core network (i.e. backhaul).In some examples, the second input data signal comprises a plurality ofsub-signals, and the apparatus may further comprise a second switchconfigured to assemble the sub-signals to form the second input datasignal.

The switching apparatus 200 may also comprise a plurality of ports 236configured to receive or output a plurality of input data signals of athird signal type, different to the first and second signal types. Thethird signal type may be subject to a delay specification, which may bethe same or a different delay specification to that applicable to thefirst signal type. The input data signals of the third signal type maybe CPRI signals exchanged between an RE and an REC or pool of RECs. Theswitching apparatus 200 may also comprise a third switch 238 configuredto multiplex the plurality of input data signals of the third signaltype into a third data signal, which in some examples is synchronisedwith the reference timing signal. The third switch may be a multiplexerand may comprise an IWF 239 configured to convert the third data signalto a packet format, such as an Ethernet format. The third switch 238 isconfigured to aggregate a plurality of CPRI signals received on theports 236, each signal corresponding to a particular RE or a particularREC. Correspondingly, when receiving data traffic over the transportnetwork, the third switch 238 is configured to separate component datasignals of the combined data signal of the third signal type, and toswitch each component data signal to the appropriate port for basebandprocessing (or radio transmission).

The switching apparatus 200 comprises a multiplexing switch 240configured to multiplex the first data signal with the second datasignal, and optionally the third data signal, if received, to form acombined data signal. The combined data signal may also be synchronisedwith the reference timing signal. The multiplexing switch 240 comprisesa framer 242 configured, for a frame of the combined data signal, tomultiplex the first, second and optionally third data signals. Themultiplexing may be a time multiplexing. The switch 240 is configured toallocate the first data signal to a portion of the frame reserved forthe first data signal. Optionally, the switch 240 is configured toallocate the third data signal to a portion of the frame reserved forthe third data signal. In some examples, the switch 240 is configured toallocate the second data signal to a remaining portion of the frame.Thus, the first, second and third data signals are allocated to apredetermined part (time slot) of the frame by the switch 240 in thesecond stage.

The multiplexing switch 240 may be a TDM switch, and may be configuredto select packets from the first and third data signals for allocationto the relevant reserved portions to ensure compliance with the delayspecification to which the first and third input signals are subject. Insome examples, the multiplexing switch 240 generates frames fortransport over a circuit switched channel, e.g. provided by transportnetwork 50. All the clients (first, second, third data signals) areframed in a single container, for example a time division multiplexedcontainer, e.g. an OTN or OTN-like container. In some aspects, theswitch 240 may be considered as an OTN/TSN switch.

The multiplexing switch 240 may schedule first, second and/or third datasignals according to one or more criteria. The first and/or third datasignals may be prioritized over the second data type, e.g. to meet thedelay and/or latency requirements. For example, the scheduling of datapackets from the first data signal and third data signal may be carriedout to ensure compliance with the appropriate delay specification, whichmay be received directly by the multiplexing switch 240 or via thetiming controller 270. The radio data of the first and/or third datasignal may be scheduled for alignment with the radio transmission (orreception) over the air interface. In some examples, the timingcontroller 270 supports the scheduling of the radio traffic.

The switching apparatus further comprises an interface 250 configured toformat the combined data signal for transmission over the transportnetwork 50 and to forward the formatted combined data signal to thetransport network. The interface 250 may provide for a configurableformat of the data signal for transmission over the transport network,e.g. selection of an optical channel or wavelength for transmission. Thetransport network may comprise a circuit switched channel, e.g. anoptical channel. A format of the second data type (e.g. Ethernet) ismaintained. As discussed above, the transport network may comprise anOTN or an OTN-like container, and the interface may be configured toformat the combined data signal for transmission over the transportnetwork. For example, the formatting may be by assigning reconfigurablewavelengths to frames of the combined data signal, or by performingother formatting appropriate to the technology of the transport network.In some examples of the disclosure, as illustrated in FIG. 4, at leastsome of the functions of the interface 250 may be incorporated into themultiplexing switch 240, such that at least some of the formatting fortransmission over the transport network is conducted within themultiplexing switch 240. Alternatively, the formatting comprises using apredetermined or static format for transmission.

As discussed above with reference to the method 100, the switchingapparatus 200 may be further configured to perform steps facilitatingreceipt of a combined data signal, extraction of the component datasignals and switching of the component data signals to their intendedrecipients. For example, the switching apparatus 200 may function as areceiving one of the hub node and remote node.

For example, and referring still to FIG. 3, the switching apparatus 200may further comprise a port 252 configured to receive a combined datasignal from the transport network 50. The interface 250 may beconfigured to format the received signal for processing and themultiplexing switch 240 may be configured to demultiplex the formattedreceived signal into a first data signal 254, a second data signal 256and a third data signal 258, and to forward the first data signal to thefirst switch 220, the second data signal to the second switch (ifpresent, not illustrated in FIG. 3), or to the port 230 configured toreceive the second data signal, and the third data signal to the thirdswitch 238. The first switch 220 may be configured to disaggregate thefirst data signal 254 into a plurality of first data signals, anddetermine the output port for a particular packet. For example, thedetermination of the output port is based on packet switching, forexample using packet header inspection, to output the plurality of firstdata signals to the corresponding plurality of ports 210. The thirdswitch 238 may be configured to demultiplex the third data signal 258into a plurality of third data signals and to output the plurality ofthird data signals to the plurality of ports 236. The third switch mayuse predetermined time division multiplexing slots to switch each of thethird data signals to the appropriate output port. The multiplexingswitch 240 may be configured to demultiplex the formatted receivedsignal by, for a frame of the formatted received data signal, extractinga packet to the first data signal from a portion of the frame reservedfor the first data signal, extracting a packet to the third data signalfrom a portion of the frame reserved for the third data signal andextracting packets to the second data signal from a remaining portion ofthe frame.

FIG. 4 illustrates an example of a switching apparatus such as theapparatus 200 of FIG. 3 when configured to act as a hub node 400, whichmay be an example of the hub node 40 of FIG. 1. Aspects and functions ofthe switching apparatus 200 are applicable to the hub node 400 unlessotherwise described. Referring to FIG. 4, the hub node 400 comprises afirst switch in the form of an MFI packet switch 420, a third switch inthe form of a MUX/DEMUX 438, which may be configured tomultiplex/demultiplex CPRI or other radio data signals, a timingcontroller 470, a multiplexing switch in the form of a TDM switch 440and an interface 450 in the form of an optical cross connect. The MFIpacket switch 420 receives MFI data signals from a plurality of modifiedRECs, or BBUs 20, via a plurality of first ports 410. The MFI packetswitch 420 then aggregates and switches MFI data from/to the BBUs.

In some examples, the switch 420 may support newly defined toolsspecified by the IEEE TSN WG. The MFI packet switch 420 is connected tothe timing controller 470 to enable support of Time Sensitive Networking(TSN) functions, for example via IEEE 1588. The timing controller mayalso support or manage statistical multiplexing within the MFI packetswitch to ensure that a delay specification for the MFI data signals,received by the timing controller from the BBU pool 20, is respected. Inalternative examples, all aspects of complying with a delayspecification may be handled between the timing controller and the TDMswitch 440. The aggregated MFI traffic signal output from the MFI packetswitch is in data packet (e.g. Ethernet) form, and is composed ofregular transmission of packets, e.g. synchronized with a referencetiming signal provided by the timing controller 470. As the timingcontroller 470 also provides the reference timing signal to the TDMswitch 440, the output aggregated MFI data stream is also synchronizedwith the TDM switch 440.

The MUX/DEMUX 438 receives radio signals, e.g. CPRI data signals, from apool of DUs 30, via third ports 436. The MUX/DEMUX then multiplexes theCPRI signals. The MUX/DEMUX 438 is also connected to the timingcontroller 470, ensuring that the output of the MUX/DEMUX 438 issynchronized with the timing reference signal.

The outputs from the MFI packet switch 420 and MUX/DEMUX 438 are inputto the TDM switch 440, together with packet backhaul traffic receivedfrom the packet router 10 via a second port 430. The TDM switch 440buffers each input signal to accommodate any difference between theinput signal clock and the timing reference signal (for example in thecase of Ethernet traffic received from the packet router 10 and which isnot already synchronised with the TDM switch via the timing referencesignal). The buffering also serves to set a delay to a valuecommunicated by the timing controller as consistent with the delayspecifications for the delay sensitive MFI and CPRI traffic. Thebuffering capacity at an ingress port of the TDM switch may bedimensioned appropriately for available bandwidth in TDM frames ascompared with incoming line speeds from the packet router 10, MFI packetswitch 420 and MUX/DEMUX 438.

FIG. 5 illustrates another example of a switching apparatus such as theapparatus 200 of FIG. 3 when configured to act as a remote node 600,which may be an example of the remote nodes 60 of FIG. 1 and maycooperate with the hub node 40, 400 of FIGS. 1 and 4. The remote node600 comprises complementary functions to the hub node 40, 400, includingoptionally an interface (not shown) which may be in the form of anoptical cross connect for an optical transport network. The remote nodemay include any corresponding function described above.

The remote node 600 comprises a multiplexing switch in the form of a TDMswitch 640. The remote node 600 further comprises a first switch in theform of an MFI packet switch 620, arranged to communicate fronthaul datawith a plurality of RBUs 70 via a plurality of first ports 610. Theremote node 600 further comprises a third switch in the form of aMUX/DEMUX 638, arranged to communicate fronthaul data with a pluralityof RRUs 80, via plurality of third ports 636. The remote node 600further comprises a second switch in the form of a data packet (e.g.Ethernet) switch 634, arranged to communicate backhaul data with aplurality of RBS 80, via plurality of second ports 630. The remote node600 further comprises a timing controller 670.

The TDM switch 640 is configured to receive an input signal from thetransport network 50, optionally via an interface (not shown), andconvert the input signal to data packet format (and CPRI format if thistraffic is carried in separate lambdas). The TDM switch 640 thenseparates out the aggregated MFI traffic, the CPRI traffic and the datapacket backhaul (e.g. Ethernet) traffic streams (i.e. first, second andthird data signals) by extracting packets from the appropriate timeslots reserved for the time sensitive traffic, and from the rest of eachframe for the Ethernet traffic. This is the reverse of the process forcombining signals performed when the switching apparatus is operating asa transmitting unit, which combining process is described in greaterdetail with reference to FIGS. 6a and 6b below. The TDM switch 640selects the most accurate clock among the inputs and provides it as areference clock to the timing control.

The remote node 600 comprises dedicated switches 620, 638 and 634 forthe first, second and third data signals respectively. The aggregatedand/or multiplexed signals are separated in the dedicated switches 620,638 and 634 and are then forwarded to the individual RBUs 70, RRUs 80and/or RBSs 90.

Thus, the fronthaul data packets received in one or more frame areidentified by the TDM switch as being of the first, second or third type(e.g. according to the time slot in which they are received). The datasignals of a particular type are forwarded to the correspondingdedicated switch 620, 638 and 634. The dedicated switch 620, 638 and 634is configured to demultiplex the received signal of a single type, andcommunicate that signal to the destination radio equipment (e.g. RBU,RRU, RBS). For example, the packet switch 620, 634 may use a packetheader to identify and switch the packets to their destination. Thedemultiplexing by the dedicated switches 620, 638 and 634 may be overone or more frames.

The remote node also functions to multiplex data from RE towards thecore network, e.g. aggregating first in the dedicated switch 620, 638and 634 (first stage), and multiplexing different types of signals inthe same frame in the TDM switch 640 (second stage). The frames are thentransmitted over the transport network 50 to the hub node.

The system architecture illustrated in FIG. 1 is optimised for a directlink connection to the remote nodes 60, 600. However, due to thestandard mapping of Ethernet over the transport network, e.g. an OTNnetwork, the system also allows for an intermediate Ethernet switch orswitches. Such switches may be incorporated on condition of compliancewith network design rules (for example a maximum of 3 hops) and supportfor proper TSN functionality. When intermediate standard packet (e.g.Ethernet) switches are implemented, the synchronous-regular packettraffic mapping would be interrupted (this can be easily detected by theremote node). However the timing critical packets should still receivelimited PDV (for example of less than 5 μs) if network design is doneproperly. The additional PDV would be handled by the remote node. Asdiscussed above, synchronisation is shared with the remote nodes via aSyncE network and a IEEE 1588 profile/architecture which depends on thetarget requirements. For the most stringent applications, a requirementfor better than 100 ns accuracy can be met by a properly designednetwork.

Operation of the TDM switch 440 is described in detail with reference toFIGS. 6a and 6b below, and results in a combined output signal which isforwarded to the interface 450 before being sent via the transportnetwork 50 to the appropriate remote node or nodes. In some examples,the interface 450 may be an optical cross connect, as mentioned above.

The timing controller 470 supports all the timing functions in the hubnode 400, providing the timing reference signal used to ensuresynchronous traffic. In addition, in some examples, the timingcontroller 470 may compare the delay specifications of all the inputsignals, received for example from the BBU pool 20 and DU pool 30, andaccordingly schedule the time slots in the TDM switch 440 to ensurecompliance with the received delay specifications. In other examples,the scheduling function may be entirely embedded in the TDM switch, withthe timing controller merely supplying the reference timing signal. Thetiming controller 470 also implements synchronization (e.g. SyncE and/orIEEE 1588) capabilities in order to support synchronous operation of theradio (e.g. CPRI) traffic, for supporting scheduling of all Radiotraffic (for alignment with radio transmission) and TSN tools.

The TDM switch 440 and timing controller 470 may apply principles setout in IEEE standards document 802.1.Qbv in multiplexing the signalsreceived from the MFI packet switch 420, MUX/DEMUX 438 and packet router10, as illustrated in FIGS. 6a and 6 b.

The first stage switches, e.g. BBU pool 20 and/or DU pool 30 areconnected to the packet switch/router 10. This allows communication ofbaseband processed signals from an RE to be transmitted to the corenetwork as backhaul by the packet switch/router 10. Similarly, thepacket switch/router 10 transmits data packets from the core network tothe BBU pool 20 and/or DU pool 30, for generation of the radio signalsto be transmitted over an air interface by an RE. The RE may provide acell connected to one or more User Equipment (e.g. mobile phone) orwireless device.

It will be appreciated that the system of FIG. 1, and elementsillustrated in FIGS. 4 and 5, have been discussed with reference totraffic flow from a core network towards remote units. Complementaryfunctions may be performed for traffic flow from the remote units to thecore, as discussed above with reference to FIGS. 2 and 3.

FIGS. 6a and 6b illustrate one way in which the multiplexing switch 240,which may for example be implemented as TDM switch 440, 640, allocatestime slots in a combined signal frame. The time slots may be allocatedat a multiple of the timing reference signal provided by the timingcontroller 470, based on information provided by the timing controllerfor each input client. The multiple may be one or more instances of thetiming reference signal. This allocation process is performed when theswitching apparatus 200, which may be configured as a hub node 400 orremote node 600, is operating as a transmitting element, forwardingtraffic to the transport network for transmission.

Referring to FIG. 6a , the TDM switch 240, 440, 640 receives first,second and optionally third input data signals for example in the formof an aggregated MFI signal 254, an Ethernet signal 256 and amultiplexed CPRI signal 258. The TDM switch 240, 440, 640 outputs acombined signal 260 for transport over the transport network, which mayfor example be an Ethernet signal encapsulated for OTN.

As shown in FIG. 6b , in each frame of the output signal (e.g.Ethernet/OTN), the TDM switch 240, 440, 640 allocates data 510 (e.g. apacket 510 a) from the aggregated MFI data stream to a time slot 540 awhich is reserved for MFI data. In some examples, the TDM switch 240,440, 640 allocates a portion, for example a packet 520 a from the radiodata (e.g. CPRI) stream e.g. following IWF conversion, to a time slot550 a reserved for this type of radio (e.g. CPRI) data. The TDM switch240, 440, 640 then fills the rest of the frame 560, e.g. as a furthertime period 560, with data 530 from the packet data backhaul (e.g.Ethernet) stream. Each time slot 540 a, 550 a or further time period 560contains only one type of data signal, e.g. first, second or third datatype. The frame may further comprise overhead (OH), e.g. for routingand/or error correction.

Each reserved slot 540 a, 550 a, e.g. for MFI data or CPRI data, isseparated from the next reserved slot for that data type 540 b, 550 b bya multiple of the timing reference signal T. By separating the differentsignal types in this way, the TDM switch 240, 440, 640 enables controlof the specific latency requirement for each traffic typology. The TDMswitch may be guided in its selection of packets from the MFI and CPRIstreams by the timing controller 270, 470, 670, to ensure compliancewith the various delay specifications which the timing controllerreceives from the BBU pool and DU pool. Further data 510 b, 520 b may betransmitted later in the same frame, or in a later frame, e.g. in slots540 b, 550 b. Each reserved slot 540 a, 550 a may comprise data for/fromone or a plurality of radio equipment (e.g. RRU, RBU, RBS). As such,each reserved slot 540 a, 550 a or remainder 560 may comprise datareceived/transmitted on one or a plurality of the first ports; or one ora plurality of the second ports; or one or a plurality of the thirdports.

The TDM switch 240, 440, 640 maintains the packet (e.g. Ethernet) formatfor possible integration of Ethernet TSN switches in the cloud betweenthe hub node 400 and the remote nodes 60. VLAN may be used to identify aspecific flow, including packetized CPRI, MFI, Ethernet etc, such thatit is possible to differentiate between individual flows within a singletraffic type. The Ethernet switching functionalities also support newbridging tools, being defined by IEEE, to cope with stringent Fronthaulrequirements, including for example the IEEE 802.1.Qbv and .qu tools.

In some examples, the TDM switch 240, 440, 640 implements a standard OTNframing with synchronous mapping in accordance with ITU-T recommendationG.709. This mapping allows the addition of an optional FEC. The TDMswitch may allocate a separate frame/lambda for legacy CPRI traffic.

As discussed above, all input data into the TDM switch 440, 640 may beEthernet based, for example if CPRI traffic is converted to Ethernetformat in IWF 439 of the MUX/DEMUX (IWF not illustrated in the MUX/DEMUX638 of FIG. 6). Alternatively, some input data may be CPRI based, inexamples in which this traffic is to be carried in separate lambdas.Such traffic may be mapped according to the Supplement to ITU-T G-seriesRecommendations—CPRI over OTN (for example section 8, Multiple CPRIoption 3, 4 or 5 signal mapping into ODU2r).

Packets relating to the timing sensitive data are allocated by the TDMswitch 240, 440, 640 at synchronous time slots, allowing all data to bemapped according to a fixed slot of a fixed size or multiple of a fixedsize corresponding to CPRI and MFI timing sensitive packet size. Inpractice a regular and periodic structure of the Ethernet frame isavailable at the input of the TDM switch 240, 440, 640 as a consequenceof both the actions of the timing controller 470, 670 in controlling theMFI packet switch and MUX/DEMUX, and of buffering actions at the ingressport of the TDM switch.

Existing CPRI traffic may be mapped as packets into the transportcontainer, e.g. via Pseudo Wire Emulation (PWE) or IWF, as defined forexample by IEEE 1904.3 and IEEEE 802.1CM, associating a timestamp forproper handling at the radio side, and carried over the same lambda asother packet based traffic. Nevertheless, CPRI traffic is considered tobe of a different type to the packet fronthaul traffic referred to asMFI, which is natively a packet fronthaul interface. Ethernet trafficmay then be mapped according to an OTN standard framing as set out inG.709, for example via a BMP mapping in the OTN frame (for example 10 GLAN→BMP→OPU2e→OTU2e) for guaranteed timing performance. The use of astandard OTN framing also allows for FEC support.

Symmetric transmission should be guaranteed for CPRI traffic via properscheduling at the end nodes, and MFI traffic should also have associatedtimestamps for proper scheduling, unless this will be taken care byhigher level (Radio) protocols.

FIG. 7 illustrates another example of switching apparatus 700 which mayimplement the method 100 or any node described, for example on receiptof suitable instructions from a computer program. Referring to FIG. 7,the switching apparatus 700 comprises a processor 701 and a memory 702.The memory 702 contains instructions executable by the processor 701such that the switching apparatus 700 is operative to conduct some orall of the steps of the method 100.

The method 100 may be implemented, for example using switching apparatus200 or 700, in a system for exchanging data signals. The system may forexample comprise a first switching apparatus acting as a hub node, asecond switching apparatus acting as a remote node and a transportnetwork coupled between the first apparatus and the second apparatus, asillustrated in FIG. 1.

Aspects of the present disclosure thus provide a layered switchingarchitecture and method in which a plurality of inputs of differentsignal types may be combined for transmission over a transport network.The method and apparatus support both “legacy” CPRI traffic and packetMFI traffic between modified REs and RECs (with L1 processing conductedat the modified RE). Jitter performance is assured by having each signaltype managed by a dedicated input switch, and strict delay and jitterrequirements for the time sensitive CPRI and MFI traffic are respected,while also ensuring bandwidth efficiency through the construction of alarge aggregate pipe formed of multiple small rate signals. The reuse ofa standard signal format, for example Ethernet and OTN, allows forstandardized OAM operations as well as interworking with Ethernet (TSN)switched networks and OTN networks.

The layered architecture proposed in examples of the present disclosureallows for different levels of prioritization and multiplexing at packetlevel (when feasible), at time slot level, and at wavelength level (forexample if timing characteristics cannot be met with the previousoptions). Packet level optimisation and prioritisation may take placevia the dedicated switches of stage 1 of the layered architecturepresented in the present disclosure. For example, aggregation at apacket level may take place in the first switch 220 of the apparatus200, which may be a MFI switch 420, 620. This aggregation may includestatistical multiplexing, offering important bandwidth efficiencies.Additional stage 1 optimisation may take place in the third switch 238,which may be a MUX/DEMUX 438, 638, and in the second switch, if present.Time slot level optimisation and prioritisation may take place in themultiplexing switch 240, of stage 2, which may be implemented as a TDMswitch 440, 640. By allocating traffic of first and third signal types(if present) to reserved time slots, and filling the rest of a framewith traffic of a second data signal type, efficient resource usage ispaired with efficient combination of different signal types, allowingfor the respect of delay requirements which may apply to the first andthird signal types. Wavelength level prioritisation and optimisation maytake place in the interface or multiplexing switch that performs theformatting of stage 3 to prepare signals for transmission over thetransport network. The possibility of segregating different vendor orsynchronization domains also ensures that such entities canindependently apply their policies (for example regarding an acceptablenumber of rejected packets) in the switches of the first stage. Eachvendor only needs to communicate to the timing controller a minimal setof data constituting the delay specification for time sensitive data.This may include for example delay and delay variation values.

The methods of the present disclosure may be implemented in hardware, oras software modules running on one or more processors. The methods mayalso be carried out according to the instructions of a computer program,and the present disclosure also provides a computer readable mediumhaving stored thereon a program for carrying out any of the methodsdescribed herein. A computer program embodying the disclosure may bestored on a computer readable medium, or it could, for example, be inthe form of a signal such as a downloadable data signal provided from anInternet website, or it could be in any other form.

It should be noted that the above-mentioned examples illustrate ratherthan limit the disclosure, and that those skilled in the art will beable to design many alternative embodiments without departing from thescope of the appended claims. The word “comprising” does not exclude thepresence of elements or steps other than those listed in a claim, “a” or“an” does not exclude a plurality, and a single processor or other unitmay fulfil the functions of several units recited in the claims. Anyreference signs in the claims shall not be construed so as to limittheir scope.

The invention claimed is:
 1. A method for switching data signalstransmitted over a transport network; the method comprising: receiving aplurality of input data signals of a first signal type, wherein theplurality of data signals of the first signal type comprises datasignals exchanged between a Radio Equipment (RE) and a Radio EquipmentController (REC); aggregating the plurality of input data signals intoan aggregated first data signal; receiving a second data signal of asecond signal type different to the first signal type; multiplexing theaggregated first data signal with the second data signal to form acombined data signal; and forwarding the combined data signal to thetransport network; wherein multiplexing the first data signal with thesecond data signal comprises, for a frame of the combined data signal:allocating the first data signal to a portion of the frame reserved forthe first data signal; and allocating the second data signal to aremaining portion of the frame, wherein the aggregated first data signaland the combined data signal are synchronised with a reference timingsignal, and/or wherein multiplexing the aggregated first data signalwith the second data signal to form a combined data signal comprisesperforming time division multiplexing of the aggregated first datasignal with the second data signal.
 2. A method as claimed in claim 1,wherein the plurality of data signals of the first signal type aresubject to a delay specification, and the second data signal of thesecond signal type is not subject to the delay specification.
 3. Amethod as claimed in claim 1, wherein the plurality of data signals ofthe first signal type and/or the data signal of the second signal typecomprise packet data signals.
 4. A method as claimed in claim 1, whereinthe second input data signal comprises a data signal exchanged between aRadio Base Station (RBS) and a core network.
 5. A method as claimed inclaim 1, wherein the second input data signal comprises a plurality ofsub-signals, and wherein the method further comprises: assembling thesub-signals to form the second input data signal.
 6. A method as claimedin claim 1, further comprising formatting the combined data signal fortransmission over the transport network.
 7. A method as claimed in claim1, wherein the transport network comprises an optical network.
 8. Amethod as claimed in claim 6, wherein the transport network comprises anoptical network; and wherein formatting the combined data signal fortransmission over the transport network comprises assigningreconfigurable wavelengths to frames of the combined data signal.
 9. Amethod as claimed in claim 1, wherein aggregating the plurality of inputdata signals of the first signal type into an aggregated first datasignal comprises performing statistical multiplexing of the plurality ofinput data signals.
 10. A method as claimed in claim 1, furthercomprising: receiving a plurality of input data signals of a thirdsignal type, different to the first and second signal types;multiplexing the plurality of input data signals of the third signaltype into a third data signal; and multiplexing the first data signalwith the second data signal and the third data signal to form thecombined data signal; wherein multiplexing the first data signal withthe second data signal and the third data signal comprises, for a frameof the combined data signal: allocating the first data signal to aportion of the frame reserved for the first data signal; allocating thethird data signal to a portion of the frame reserved for the third datasignal; and allocating the second data signal to a remaining portion ofthe frame.
 11. A method as claimed in claim 10, wherein the plurality ofinput data signals of a third signal type are subject to a delayspecification, and/or the plurality of input data signals of the thirdsignal type comprises data signals exchanged between an RE and an REC.12. A method as claimed in claim 10, wherein the plurality of input datasignals of the third signal type comprise Common Public Radio Interface(CPRI) data signals.
 13. A method as claimed in claim 10, furthercomprising receiving a combined input data signal and separating thecombined input data signal into a first input data signal comprising theplurality of input data signals of a first signal type, a second inputdata signal comprising the data signal of a second signal type and athird input data signal comprising the plurality of input data signalsof the third signal type.
 14. An apparatus for switching data signalstransmitted over a transport network, the apparatus comprising: aplurality of first ports configured to receive a plurality of input datasignals of a first signal type which are exchanged between a RadioEquipment (RE) and a Radio Equipment Controller (REC); a first switchconfigured to aggregate the plurality of input data signals into anaggregated first data signal; a second port configured to receive asecond data signal of a second signal type different to the first signaltype; a multiplexing switch configured to multiplex the aggregated firstdata signal with the second data signal to form a combined data signal;and an interface configured to forward the formatted combined datasignal to the transport network; wherein the multiplexing switchcomprises a framer configured, for a frame of the combined data signal,to multiplex the first and second data signals by: allocating the firstdata signal to a portion of the frame reserved for the first datasignal; and allocating the second data signal to a remaining portion ofthe frame, wherein the apparatus further comprises a timing functionconfigured to provide a reference signal, wherein the first switch isconfigured to aggregate the plurality of input data signals into anaggregated first data signal which is synchronised with the referencesignal, and the multiplexing switch is configured to multiplex theaggregated first data signal with the second data signal to form acombined data signal which is synchronised with the reference signal,and/or wherein the multiplexing switch is configured to multiplex theaggregated first data signal with the second data signal via timedivision multiplexing.
 15. The apparatus as claimed in claim 14, whereinthe plurality of input data signals of the first signal type are subjectto a delay specification, and the second data signal of the secondsignal type is not subject to the delay specification.
 16. The apparatusas claimed in claim 14, wherein the second signal type is exchangedbetween a Radio Base Station (RBS) and a core network.
 17. The apparatusas claimed in claim 14, wherein the second input data signal comprises aplurality of sub-signals, and wherein the apparatus further comprises asecond switch configured to assemble the sub-signals to form the secondinput data signal.
 18. The apparatus as claimed in claim 14, wherein thefirst switch is configured to aggregate the plurality of input datasignals of the first signal type into an aggregated first data signal byperforming statistical multiplexing of the plurality of input datasignals.
 19. The apparatus as claimed in claim 14, further comprising: aplurality of third ports configured to receive a plurality of input datasignals of a third signal type, different to the first and second signaltypes; and a third switch configured to multiplex the plurality of inputdata signals of the third signal type into a third data signal; whereinthe multiplexing switch is configured to multiplex the first data signalwith the second data signal and the third data signal to form thecombined data signal; and wherein the framer is configured to multiplexthe first, second and third data signals by, for a frame of the combineddata signal: allocating the first data signal to a portion of the framereserved for the first data signal; allocating the third data signal toa portion of the frame reserved for the third data signal; andallocating the second data signal to a remaining portion of the frame.20. The apparatus as claimed in claim 19, wherein the third data signalof the third signal type is exchanged between an RE and an REC.
 21. Anapparatus for switching data signals transmitted over a transportnetwork; the apparatus comprising a processor and a memory, the memorycontaining instructions executable by the processor whereby theapparatus is operative to: receive a plurality of input data signals ofa first signal type wherein the plurality of data signals of the firstsignal type comprises data signals exchanged between a Radio Equipment(RE) and a Radio Equipment Controller (REC); aggregate the plurality ofinput data signals into an aggregated first data signal; receive asecond data signal of a second signal type different to the first signaltype; multiplex the first data signal with the second data signal toform a combined data signal; and forward the combined data signal to thetransport network; wherein multiplexing the first data signal with thesecond data signal comprises, for a frame of the combined data signal:allocating the first data signal to a portion of the frame reserved forthe first data signal; and allocating the second data signal to aremaining portion of the frame, wherein the aggregated first data signaland the combined data signal are synchronised with a reference timingsignal, and/or wherein multiplexing the aggregated first data signalwith the second data signal to form a combined data signal comprisesperforming time division multiplexing of the aggregated first datasignal with the second data signal.
 22. A system for exchanging datasignals, the system comprising: a first apparatus as claimed in claim14, the first apparatus configured as a hub node and operable to receiveinput data signals from a Radio Equipment Controller (REC) and a router;a second apparatus, the second apparatus configured as a remote node andoperable to receive input data signals from a Radio Equipment (RE) and aRadio Base Station (RBS); and a transport network coupled between thefirst apparatus and the second apparatus, wherein the first apparatus isconfigured to transmit data signals of the first and second type overthe transport network to the second apparatus, and the second apparatusis configured to transmit data signals of the first and second type overthe transport network to the first apparatus, wherein the secondapparatus comprises: a plurality of first ports configured to receive aplurality of input data signals of a first signal type which areexchanged between a Radio Equipment (RE) and a Radio EquipmentController (REC); a first switch configured to aggregate the pluralityof input data signals into an aggregated first data signal; a secondport configured to receive a second data signal of a second signal typedifferent to the first signal type; a multiplexing switch configured tomultiplex the aggregated first data signal with the second data signalto form a combined data signal; and an interface configured to forwardthe formatted combined data signal to the transport network; wherein themultiplexing switch comprises a framer configured, for a frame of thecombined data signal, to multiplex the first and second data signals by:allocating the first data signal to a portion of the frame reserved forthe first data signal; and allocating the second data signal to aremaining portion of the frame.
 23. A nontransitory computer readablestorage medium comprising computer program instructions which, whenexecuted on at least one processor, cause the at least one processor tocarry out a method for switching data signals transmitted over atransport network; the method comprising: receiving a plurality of inputdata signals of a first signal type, wherein the plurality of datasignals of the first signal type comprises data signals exchangedbetween a Radio Equipment (RE) and a Radio Equipment Controller (REC);aggregating the plurality of input data signals into an aggregated firstdata signal; receiving a second data signal of a second signal typedifferent to the first signal type; multiplexing the aggregated firstdata signal with the second data signal to form a combined data signal;and forwarding the combined data signal to the transport network;wherein multiplexing the first data signal with the second data signalcomprises, for a frame of the combined data signal: allocating the firstdata signal to a portion of the frame reserved for the first datasignal; and allocating the second data signal to a remaining portion ofthe frame, wherein the aggregated first data signal and the combineddata signal are synchronised with a reference timing signal, and/orwherein multiplexing the aggregated first data signal with the seconddata signal to form a combined data signal comprises performing timedivision multiplexing of the aggregated first data signal with thesecond data signal.